1. Technical Field
Embodiments relate to semiconductor devices and, more particularly, to semiconductor devices operated by internal clock signals.
2. Related Art
Semiconductor devices, for example, dynamic random access memory (DRAM) devices may be designed to operate at a high speed with low power consumption and large cell capacitance. Thus, most semiconductor devices may be designed to have a power-down mode that minimizes a driving current when data is not being accessed. In general, semiconductor devices may be released from the power-down mode if a clock enable signal is enabled and inputted even in the power-down mode.
The semiconductor devices may still communicate with external chip set devices using the clock enable signal even though the semiconductor devices are in the power-down mode. The clock enable signal may act as a reference signal that determines whether a clock signal outputted from the external chip set devices should be applied to internal circuits of the semiconductor devices. The semiconductor devices may transmit the clock signal to the internal circuits thereof only when the clock enable signal is activated. That is, the semiconductor devices typically do not transmit the clock signal to the internal circuits thereof when the clock enable signal is inactivated. The semiconductor devices may execute a data access operation when the clock signal is transmitted to the internal circuits of the semiconductor devices.
Meanwhile, each of the semiconductor devices may generate a plurality of internal clock signals having different phases to operate at a high speed and may input or output data using the plurality of internal clock signals. For example, if at least two internal clock signals are generated in each of the semiconductor devices and are used to receive or output data, the semiconductor devices may operate at a higher speed as compared with other semiconductor devices directly operated using an external clock signal. When a plurality of internal clock signals are used in each semiconductor device, it may be necessary to reset starting points of time and terminating points of time of a plurality of control operations including the power-down mode using the internal clock signals as reference signals.